The overall objective of this project is to develop novel monoclonal antibody radionuclide conjugates and to increase potential of anti-tumor efficacy of radiolabeled MAb GA22-2 directed against the gastrointestinal tumor associated 185 kDa glycoprotein. MAb GA22-2 of the IgG1 isotype and its IgG2a switch variant were selected, since the GA22-2 antigen has highly restricted distribution in the gastrointestinal tumors with virtually no MAb crossreactivities with normal human tissues. To improve the MAb's half-life in man and its utility for radionuclide coupling, the chimeric molecules will be constructed with human heavy chain gamma 1 genes and then modified with human metallothionein gene and with a nucleotide sequence which will encode for e peptides capable of binding several bifunctional chelates or gold clusters (Project 1). Two radionucleides with appropriate crossfire beta irradiation to overcome antigen heterogeneity, and with some gamma emissions for in vivo detection were selected (Project 2). 57Cu with t1/2=61.9h, beta E=141 keV and gamma E=184.6 keV and 153Sm with t1/2, 46.7h beta E=280 keV and gamma E=103 keV are proposed as well suited radioisotopes, which will be prepared at a high specific activity under Project 2. Furthermore, under Project 2, new complexation procedures will be developed by modifying chelates DOTA, TETA and CDTA, which will involve functionalization of the macrocycles with a cyclohexyl group to preorient the ring in order to accept Sm. For 67Cu the metallothionein chimeric MAb developed under Project 1 will be used. The third radioisotope 199Au with t1/2=3.1 d, beta E = 296 keV and gamma E = 158 keV will be developed using covalently linked stable clusters of gold atoms (Project 3) for MAb conjugation. The modified, cystein and/or lysine rich constructs of MAb GA22-2 developed under Project 1 are expected to improve gold cluster linkage. High specific activity 199Au production will be developed at Brookhaven National Laboratory in the High Flux Beam Reactor under Projects 2 and 3. Radioimmunoconjugates developed and characterized under Projects 2 and 3 will be studied at the Principal Investigators' laboratory for the final evaluation of biodistribution, dosimetry and radioimmunotherapy in vivo in xenografted nude mice. It is expected that this cooperative program between two institutions and four laboratories will lead to the development of improved radioimmunotherapy of gastrointestinal cancer.